Viscosity of Petroleum Products Viscosity-Temperature Characteristics of Pennsylvania Lubricating Oils'
N E of t h e
The kinematic viscosities at 210' and 100' F. of a large number of closely fractionated, blended, and commercial grades of Pennsylvania oils have been determined accurately in modified Ostwald viscometers. The relation between the kinematic viscosity at 100' F. (KV,,) and the viscosity at 210' F. (KV,,,) is expressed by the equation :
n e a r l y a l l of these are based most imporon the Saybolt viscosity of the oils. The accuracy with which tant s i n g l e characteristics of lubricatingoil Saybolt v i s co s i t y m e a s u r e ments can be made is generis the rate of change of viscosity with temperature as related to ally conceded to be about * 1 per cent, and, a l t h o u g h n o its actual viscosity. A number of methods have been devised for appreciable d i f f e r en c e is inc o r p o r a t e d i n the calculated e x p r e s s i n g the viscosity-temperature coefficient of oils, based viscosity index in the case of very viscous oils, the error in either on the slope of a line drawn on a viscosity-temperaviscosity index introduced by From existing data a similar equation is ture plot, such as the A. S. T. M. small errors in the v i s c o s i t y derived for typical naphthenic oils : chart ( 2 , 6 ) ,or on the comparison measurements of light oils is with standard reference oils havgreatly magnified b e c a u s e c, f ing arbitrarily fixed coefficients the convergence of the curves in this r e g i o n . T h i s f a c t was (6, 8). If the coefficient is deO n the basis of these equations, complete recognized by the original infined from a purely theoretical viscosity index tables have been constructed standpoint, it loses some of its vestigators and the data were practical significance because of later revised by Davis, Lapeyexpressed in absolute viscosity units. For the fact that the rate of change r o u s e , a n d D e a n (6) for the purposes of identification it is suggested region of oils having viscosities of viscosity with temperature that this method be called "kinematic visbelow 50 S a y b o l t s e c o n d s a t varies with the type of oil, the cosity index." temperature, and the viscosity. 210°F. They advised the use of modified Ostwald viscomeConsequently, numerical values of the (dq/dt) term for different R. E. HERSH, E. K. FISHER, A N D M. R. FENSKE ters for the accurate measureoils could be compared, strictly ment of the viscosities of light Pennsylvania State College, speaking, only a t the same temoils and based the r e v i s i o n of State College, Pa. peratures and in case the viscosithe original data on the converted kinematic viscositv obties of the oils were equal. The system developed Iiy Dean and Davis ( 8 ) for the tained for the oils in this region. The method by whiih the classification of lubricating oils according to viscosity index conversion from kinematic viscosity to Universal Saybolt eliminates the effect of these variables to a large extent. seconds was effected, however, was not included in the article, These investigators found that "the viscosity indexes of all and without this knowledge the research worker has a choice lubricating fractions, separated or refined by conventional of a number of conversion formulas, each of which results in methods from any given crude, ordinarily are approximately a slightly different value for the calculated viscosity index. constant." On this basis two series of lubricating oil samples, In research or identification work the importance of accurate representing extreme types with respect to viscosity-temperaviscometry methods is obvious, and i t follows directly that ture coefficient, were chosen as standards for the comparison reliable and uniformly accepted methods for converting of oils from various sources. kinematic viscosity to Saybolt seconds are equally important The convenience and usefulness of this system of classifiin determining the viscosity index. cation is widely recognized by petroleum technologists. The The latter difficulty can be entirely eliminated by preparing viscosity index immediately gives a means of identification viscosity index tables expressed in terms of kinematic visas to source and lends itself readily to the correlation of cosity. This system appears to be the most desirable since performance data, such as the effect of the type of oil on the the expression of viscosity in fundamental units is advantaease of cold weather starting (3, 11, 14), pumpability ( I ) , geous both from the standpoints of accuracy and practical and on consumption (14). That the viscosity index is a engineering significance. Docksey, Hands, and Hayward characteristic property of the oil is further exemplified by its (9) have constructed viscosity index charts based on the data relation to the chemical structure (7') and the molecular of Dean and Davis (8) for estimating this coefficient from the weight of the oil ( I O ) . kinematic viscosities of an oil at the temperatures usually Various investigators have prepared convenient charts employed in England and on the Continent-namely, 100" F. (37.78" C.) and 200" F. (93.33" C.), and 122" F. and extended tables for calculating the viscosity index, but 1 For previous papere In thin series, see literature citation8 18 and IS. (50" C.) and 212" F. (100" C.), respectively. A similar 1441
1442
INDUSTRIAL AND ENGINEERIKG CHEMISTRY
VOL. 27, NO. 12
%yWt Viscosity at IDOOF - Secmds
1
4
I 6 810
20
40
WBOXXI
2M
4% 6wBMMo
i(/nernat/c V,scosiiy at IWY
FIGURE1.
VISCOSITY
- Qntisto&es
4wowW
CH4RACTERISTICS O F T Y P I C ~N4PHTHENE L PENUSYLV.4NI.4 OILS
method of expressing viscoPity index in terms of the kinematic viscosities a t the temperatures conventionally used by the petroleum industry in this country-namely, 100°F.(37.780C.) and 210" F. (98.89" C.)-would prove valuable to petroleum technologists. The establishment of such a basis, however, requires the proper correlation of the available data on the standard reference oils.
Experimental Work In connection with research on Pennsylvania oils a large number of lubricating oils obtained from many different sources in the Pennsylvania area have been fractionated in efficient columns under high vacuum. The products obtained by fractionation averaged from 3 to 6 per cent of the original charge to the still and had boiling ranges a t 10 mm. of mercury absolute pressure of about 15" t o 25" F. (8" to 14" C.) between the initial and the 90 per cent boiling points. The viscosities of these fractions were determined accurately at 100" F. (37.78" C.) and 210" F. (98.89" C.) by means of modified Ostwald pipets. The standardization of these viscometers has been described in previous papers (4, 16). I n addition, the viscosities of numerous commercial oils, distillates, blends, and residuums prepared from a variety of Pennsylvania crudes were determined. The qelection of these oils was based primarily on securing representative and average samples from the various Pennsylvania fields. It is a recognized fact that the viscosity index is somewhat dependent on the wax content of the oil, since for some paraffin waxes the viscosity indexes are as high as 200. To eliminate this effect to a large extent, the samples were chosen so that the range in pour points did not extend over 50" F. (27.8" C.), the average pour points of the oils being 20" to 30" F. (-6.7" to -1.l"C.). All of the oils used for this project were conventionally refined-that is, prepared by the usual methods of distillation, dewaxing, and clay filtration. Oils receiving any chemical treatment, or solvent extraction, or addition of materials foreign t o the source, were carefully avoided. The samples selected covered practically the entire range of viscosity for lubricating oils. A representative portion of the data obtained is given in Table I. The relation between the kinematic viscosity a t 100" F. (KVloo)and the kinematic viscosity a t 210" F. (KV210)can be erpressed quite accurately by the equation:
iOO#
4ND
W#
403%
TYPICAL
The fourth column in Table I gives the value of the kinematic viscosity a t 100" F. calculated from the viscosity a t 210" F. by Equation 1, and column 5 shows the percentage deviation of this calculated value from the experimental data. The average algebraic deviation of the calculated values from the actual values for the total of 230 Pennsylvania oil samples is -0.02 per cent; the average arithmetic deviation is 1.27 per cent, equally liable t o be plus or minus, and the range of deviation falls between the limits of +4.83 to -4.67 per cent. These data were plotted on a large graph, the logarithm of the kinematic viscosity a t 100" F. being plotted against the logarithm of the kinematic viscosity a t 210" F. A reproduction of the curve obtained is shown in Figure 1 and indicated as "Viscosity Index = 100." The data given by Davis, Lapeyrouse, and Dean (6) for their series H oil was also plotted on the same graph. Conversion from Saybolt seconds to kinematic viscosity was effected by means of an experimentally established relation described in a previous paper ( I S ) . In addition, points calculated from an equation proposed by Standard Oil Development Company (15) for expressing the kinematic viscosity a t 100" F. as a function of the kinematic viscosity a t 210' F. were also included on the graph. This relation, found to correlate their experimental results satisfactorily in the less viscous range (below 6 centistokes, or 45 Saybolt seconds), is given by the following equation, expressed in centistokes: KVtoo = 2.204(KVzio)1.64
(2)
For the sake of clarity some of the experimental and calculated points have been omitted from Figure l, but a sufficient number are included to indicate the general agreement of the data for this series of oil. Because of this agreement and the fact that the curve consists of practically a weighted mean average of available published data, it was thought justifiable to accept Equation 1 as representative of the viscosity characteristics of typical Pennsylvania oils, or the 100 viscosity index series. Similarly, the lower curve on Figure 1 represents the viscosity characteristics of a typical naphthene base oil. This curve is based on the original data of Davis, Lapeyrouse, and
DECEMBER, 1935
INDUSTRIAL AND ENGIKEERING CHEMISTRY TaBLE
Oil No. 1
2 3 4 5
Kinematio Viscosity, Centirtokesa 210° F. 100' F. 3.31 16.12 3.36 16.46 3.41 16,94 3.53 17.53 3.54 17.60
I.
VISCOSITY CHARACTERISTICS O F PENNSYLVASIA OILS
Percentage Calcd. Deviation ~ i ~ of ~Calcd, ~ Viscosity Value froni a t 100' F . b Exptl. 16.14 +0.12 16.53 f O 43 16.93 -0.06 17.88 +1.99 17.97 f2.10
~ t i Viscosity Index C 100.2 101.6 99.8 106.9 107.1
~ Oil No. 86 87 88 89 90
Kinematic Viecosity, Centistokesa 210° F. looo F. 5.89 39,30 5 95 40 16 5.95 40.20 5.95 40.55 5.97 40.99
6 7 8 9 10
3.65 3.65 3.73 R 75 3,i8
18.7i 19,oo 19.35 19 68 19.88
18.87
18.87 19.52 19.69 19.94
+0.53 -0 68 +O 88 +O 05 +0.30
101.8 97.7 102.8 100.2 101.0
91 92 93 94 95
5.98 6.01 6.04
11 12 13 14 15
3.79 3.81 3.81 3.84 3.86
19.75 19.81 20.19 20 45' 20 90
20.03 20.20 20.20 20.45 20.61
+1.42 4-1.96 +o 05 0 -1.39
104.3 105 9 100.1 100.0 95.6
16 17 18 19 20
3.87 3.87 3.88 3.89 3.90
20 i o 21.01 20 52 20.91 21.05
20 70 20.70 20.78 20.87 20 95
0 -1.47 +l.26 -0.19 -0.48
21 22 23 24 25
3.93 3.96 3.99 4.01 4.06
20.86 21.55 21 29 21.79 22.31
21.20 21.46 21 72 21.88 22.32
26 27 28
4.07 4.09 4.10 4.11 4.11
'22.96 23.10 22.53 22.55 22 60
22,41 22.57 22.66 22.75 22.75
29 30
1443
Percentage Calcd. Deviation ~ ( i ~ ~of calcd, ~ ~ t i ~ Viscositv Value f r o m Visrority a t 100' F.b Exptl. IndexC 39.66 +0.92 101.9 40 27 +0.27 100.6 40.27 +0.17 100.4 40.27 -0.69 98.6 40.48 -1.24 97.5
6.13
40.16 41.00 40 63 42 37 42.57
40.58 40.90 41.21 41.84 42.15
+1.04 -0.24 -1.03 -1 25 -0.99
102.1 99.6 102.8 97.8 98.0
96 97 98 99 100
6.14 6.18 6.43 6.43 6.45
43.03 42.38 45,39 45 20 45.78
42.25 42.68 45.34 45.34 45.55
-1.81 +0.71 -0.11 f0.31 -0.50
96.4 101.7 99.8 100.6 99.1
100.0 95.3 103.9 99.4 98.5
101 102 103 104 105
6 51 6.52 6.57 6.58 6.59
47.12 46.62 47.57 47.25 46.81
46.20 46.31 46.85 46.95 47.06
-1.95 -0.66 -1.51 -0.63 +0.53
96.3 98.7 97.1 98.8 101.0
+1.63 -0 42 f 2 02 f0.41 f0.05
105.0 98.6 106 0 101.4 100.1
106 107 108 109 110
6.62 6.62 6.74 6.75 6.97
47.61 48.41 49.71 49.42 51.75
47.40 47.40 48.71 48.82 51.25
-0.44 -2.09 -2.03 -1.21 -0.97
99.1 96.0 96.2 97.7 98.3
-2.39 -2 29 58 +O 89 +O 66
92.7 93.1 101.7 102.6 101.9
111 112 113 114 115
6.98 7.16 7.17 7.20 7.30
50.91 53.82 53.97 54.53 56.32
51.36 53.39 53.51 53.84 54.99
4-0.89 -0.80 -0.85 -1.26 -2.36
101.6 98.6 98.5 97.8 95.8
116 117 118 119 120
7.36 7.45 7.49 7.51 7.60
55.95 57.36 58.32 56,65 57.55
55.67 56.71 57.17 57.40 58.44
-0.50 -1.13 -1.97 +1.32 +1.54
99.1 98.0 95.6 102.2 102.5
121 122 123 124 125
7.60 7.61 7.63 7.82 8.03
58,85 57.52 58.01 60.05 65.00
58.44 58.79 61.03 63.53
-0,70 +1.79 +1.34 fl.63 -2.26
98.8 102.9 102.5 102.6 96.3
126 127 128 129 130
8.04 8.14 8.15 8.24 8.28
64.21 65.88 64.88 65.17 67.75
63.65 64.82 64.94 66.03 66.52
-0.87 -1.61 f0.09 f1.32 -1.81
98.7 97.4 101.0 102.2 97.1
131 132 133 134 135
8.32 8.43 8.71 8.72 8.73
66,24 71.72 72.51 72,53 70.22
67.00 68.37 71.83 71.96 72.08
$1.15 -4.67 -0.94 -0,79 +2.25
101.8 93.3 98.7 98.8 103.9
136 137 138 139 140
8.91 8.99 9 02 9.19 9.35
75 12 74.01 (5.60 78.83 80.58
74.34 75.35 75.73 77.90 79.95
-1.04 +1.81 +0.17 -1.18 -0.78
98.6 102.7 100.2 98.2 98.9
141 142 143 144 145
9.74 9.82 9.83 10.07 10.09
88.76 83.38 83.38 89.30 87.22
85.04 86.09 86.22 89.47 89.73
-4.19 f3.25 4-3.41 i-0.19 i-2.88
94.0 104.2 104.5 100.3 103.7
146 147 148 149
10.27 10 28 10.44 10.52
91.15 93.61 91.80 92.82
92.15 92.29 94.45 95.54
fl.10 -1.41 +2.89 4-2.94
101.4 98.1 103.7 103.7
150 151 152 153 154
10.62 10.80 10.89 10.98 11.00
99.22 103.6 99.43 100.3 100.5
97.18 99.39 100.6 101.9 102.2
-2.06 -4.06 +l.lB f1.59 4-1.69
96.9 94.6 101.6 101.9 102.1
155 156 157 158
11.02 11.25 11.44 11.60
103.6 107.6 104,9 109.3
102.5 106.0 108.4 110.7
-1.06 -1.49 f3.34 f1.28
98.6 97.8 103.9 101.5
+O
6.10
~~
31 32 33 34 35
4.14 4.17 4.22 4.30 4 30
23,45 23,35 23.85 24,05 24.12
23.01 23.27 23.71 24.41 24 41
-1.87 -0.34 -0.59 +1.49 +l.20
94.5 99.0 98.2 104.1 103.3
36 37 38 39 40
4 4 4 4 4
31 33 36 36 46
24 25 24 25
48 06 90 13 26 28
24 24 24 24 25
51 68 95 95 84
+o -0 -1
12 51 20 72 67
100 95 100 98 95
41 42 43 44 45
4 4 4 4 4
47 48 52 54 60
25 25 26 26 26
80 82
93 02 30 56
+O
50
10 83 88
25 26 26 26 27
101 102 102 97 102
46 47 48 49 50
4 4 4 4 4
62 68 76 78 80
27 27 28 28 29
44 69 72 83 23
27 27 28 28 28
29
51 52 53 54 55
4.81 4.85 4 89 4.99 5.00
28.81 29.46 29.97 30.93 31.00
56 57 60
5 05 5.08 5.15 5.16 5 18
61 62 63 64 65 66 67 68 69 70
11
-1
+O
+ O 81 + O 77 -1 00 +O
86
2 8 5 0 6
5 1
9 4 2
58.55
-0 55 58 -0 49 -0 17 -0 92
98 6 101 3 q8 8 99 5 97 8
29.05 29.43 29.80 30.75 30.84
+0.83 -0.10 -0,57 -0.58 -0 52
102 1 99.8 98.6 98.5 98.8
31.45 31.62 31.94 32.68 32.12
31.32 31.61 32.27 32.37 32.57
-0.41 -0 03 +1.03 -0 95 +1 40
99.0 99.9 102.4 97.8 103.2
5.24 5.24 5.24 5.28 5.47
32.86 33.00 33.60 33.53 35 47
33.15 33.15 3.7.15 33 54 35 41
+ O 88 +0.45 -1.34 +0.03 -0 17
102.0 101.0 96.9 100.1 99.7
5.66
5.51 5.60
5.70 5.70
35.82 36.47 37.17 37.61 37.74
35.81 36.22 37.31 37.72 37.72
-0.03 -0.69 +0.38 4-0.29 -0 05
99.4 101.4 100.9 100 6 99.9
71 72 73 74 75
5.73 5.73 5.75 5.76 5.78
31.50 37.74 37.80 38.40 38.05
38.02 38.02 38.22 38.32 38.54
f1.38 +0.74 4-1.11 -0.21 +1.28
102.9 101.6 102.4 99 6 102.6
159 160 161 162
11.90 12.14 12.17 12.37
114.7 115.6 116 6 118 5
115.0 118.5 118 9 121.9
+0.03 +2.51 +1.97 +2.87
100.3 102.9 102.3 103.2
76 77 78 79 80
5.79 5.79 5.79 5.79 5.79
38.14 38.38 38.40 38.44 38.87
38.64 38.64 38.64 38.64 38.64
+1.31 i-0.68 f0.63 +0.52 -0.59
102.7 101.4 101.3 101.1 98.8
163 164 165 166 167
12.82 13.05 13,32 13.47 13.67
128.7 131.3 133.6 139.7 138.0
128.6 132.1 136.2 138.5 141.6
+0.61 +1.95 -0.86 +2,61
-0.01
99.9 100.7 102.2 99.0 102.8
81 82 83 84 85
5.82 5.86
39.47 38.93 39.04 39.30 39.82
38.94 39.35 39.35 39.35 39,46
-1 34 f1.08 + O 79 fO.13 -0.90
97.2 102.2 101 6 100.3 98.1
168 169
13.74 13.93 13.93 13.97 13.99
148.9 144.1 145.8 142.0 147.1
142.7 145.7 145.7 146.3 146.6
-4,16 fl.11 -0.01 4-3.02 -0.34
95.3 101.2 99.9 103.2 99.7
58 59
5.86
5.86 5.87
85
58 78 96
fO
170 171
172
INDUSTRIAL AND ENGINEERING CHEMISTRY
1444
VOL. 27, NO. 12
TABLE I (Continued) Oil
No. 173 174 175 176 177
Kinematic ViscositY, Centistokesa 100° F. 210° F. 148.5 14.01 144.1 14.03 150.5 14.06 148.0 14.15 154.8 14.20
Calcd. KinemFtic Viscosity a t 100' F . b 147.1 147.4 147.9 149.2 150.0
Percentage Deviation of Calcd. Value from Exptl. -0.94 4-2.28 -1.73 iO.81 -3.10
178 179 180 181 182
14.45 14,76 14.81 14.95 14.99
151.0 161.2 163.7 166.4 159.7
154.1 159.1 159.9 162.2 162.8
+2.05 -1.30 -2.32 -2.52 +l.94
183 184 185 186
15.23 15.44 16.30 17.13
164.0 171.4 185.8 201.4
166.7 170.2 184.6 198.9
$1.64 -0.70 -0.65 -1.24
187 188 189 190 191
17,20 17.22 17.79 18.52 20.39
195.8 197.9 214.1 223.7 253.5
200.1 200.5 210.5 223.7 258.3
+2.19 4-1.31 -1.68 0 +1.89
192 193 194 195 196
20.61 21.18 21.78 21.88 21.91
258.3 270.7 284.7 288.5 282.5
262.6 273.5 285.2 287.2 287.8
11.66 11.03 +0.18 -0.45 +1.87
333.8 338.6 361.2 414.3 473.4
325.2 340.7 363.7 412.5 455.9
-2,58 4-0.62 S0.69 -0.44 -3.70
Viscosity IndexC 99.0 102.4 98.1 100.9 96.6
Oil
No. 202 203 204 205 206
23.77 197 24.52 198 25.61 199 27.85 200 29.77 201 a Actual ex erimental valuea obtained in modified Ostwald viacometere. b Calculate$ by Equatlon 1. c Calculated from Table 111.
Dean (6)in the more viscous range. The extrapolation for oils of low viscosity was made with the aid of the equation: (3)
for expressing the kinematic viscosity at 100' F. in terms of the kinematic viscosity at 210" F., measured in centistokes, of a zero viscosity index oil (16). The line drawn through the points was considered to be the best average of the data. This curve, representing the zero viscosity index base line, can be expressed by the following equation: (4)
TABLE 11.
PHYSICAL PROPERTIES O F
Kinematic Viscosity, Centistokee" 210' F. 100' F. 487.3 31.23 496.9 31.58 504.7 31.60 511.4 31.90 520.5 32.05
Calcd. Kinematic Viscosity at 1 O O O F . b 490.1 498.3 498.8 505.9 509.5
Percentage Deviatioh of Calcd. Value from Exptl. +0.57 +0.26 -1.17 -1.07 -2.11
Viscosity Index6 100.4 100.2 99.2 99.2 98.5
-0.99 -0.80 -4.42 -1.30
99.3 99.5 96.9 99.1
-2.18
-0.76 -0.78 -0.94
98.4 99.3 99.5 98.5 99.4
10.66 -0.17 -1.82
100.4 99.9 98.8
33.71 33.94 33.99 34.12
555.1 559.7 582.2 567.1
549.6 555.2 556.5 559.7
34.74 34.77 36.64 36.75 37.18
588.8 581.8 627.6 630.5 642.6
576.0 575.7 622.8 625,.6 636.6
37.78 37.88 37.89
647.8 655.8 667.4
652.1 654.7 654.9
38.87 40.52 40.75 43.93 47.28 47.78
699.1 752.2 755.8 795.6 938.5 904.3
-1.05
9s.3 97.7 97.9 101.6 98.4 101.4
52.74 58.71 82.44 119.2 173.9
1067 1211 2005 3542 6400
1076 1263 2102 3655 6440
+0.85 +4.29 +4.83 +3.19 +0.69
100.4 101.2 102.0 101.2 100.2
181,5
7038
7108
+0.99
100.3
where K ~ I O=Okinematic viscosity at 100" F., centistokes KV~IO = kinematic viscosity at 210" F., centistokes An attempt was made to establish this curve by actual experimental data obtained by fractionating a coastal oil supposedly definitely related to the oil used by Dean and Davis (8) in establishing the original zero viscosity index data. The physical properties of this oil, and the fractions are given in Table 11. The fractionation of this oil was carried out in a 10-foot column operated a t very low pressures. No evidence of cracking was noticed during the distillation as indicated by the coGr, odor, and vacuum-Engler curves of each of the fractions. Vacuum-Engler distillation tests a t 10 mm. of mercury absolute pressure on the fractions showed
FRACTIONS FROM VACUUM
FRICTIOXITION OF FROM SUGl.4RLAND CRUDE
5 GALLONS OF
COASTAL O I L
(Operating conditions: absolute pressure top of column, 0.34 mm. mercury: reflux ratio, 5 : l (overflow t o product); average rate of product removal, 1 quart Der hour) wt.% of Charge Refractive Saybolt Viscosityb Viscosity Gravit Viscosity Index a t 50% B. P. Kinematic Viscosity Total In 210° F. looo F. IndexC Indexdl 100" F. Index" Gravity Z O O C. a t 10 Mm. 210° F. distilled C u t No. fraction A. P.I. ng a F. Centistoke6 4 50.3 431.8 0 24 93.75 21.0 1.5084 499 7.66 80.4 28 35.7 15.90 1.5103
